Friday, 29 May 2015

Temperature's rising: expert says dinosaurs were warm-blooded

Dinosaurs, those
bygone masters of the planet, were warm-blooded just like today's
mammals, according to a scientist who judged their metabolism using body
mass and growth rates deduced from fossils of species including
Tyrannosaurus rex.Paleontologist
Michael D'Emic of Stony Brook University in New York took issue with
the conclusion of other researchers last year that dinosaurs were
neither cold-blooded nor warm-blooded, but had a metabolism somewhere in
between.Scientists have
debated since the 19th century whether dinosaurs were slow, lumbering,
cold-blooded creatures, as originally thought, or boasted a more
warm-blooded physiology allowing for a vigorous lifestyle."The
main point of my study is that the dinosaurs that have been studied so
far were on average as warm-blooded as mammals living today," said
D'Emic, who argued that the 2014 study under-estimated dinosaur growth
rates and should have analyzed dinosaurs statistically within the same
group as today's birds.Birds, which evolved from small feathered dinosaurs roughly 150 million years ago, are warm-blooded.The
researchers in last year's study evaluated the metabolism of 21 dinosaur
species using a formula based on their body mass, as revealed by the
bulk of their thigh bones, and their growth rates, indicated by growth
rings in fossil bones akin to those in trees. The species included
predators like T. rex, long-necked and duckbilled plant-eaters and
others.They compared this information to data on living mammals, birds, fish and reptiles.D'Emic re-analyzed the same data to reach his conclusions, published in the journal Science.The
authors of last year's study on Thursday disputed D'Emic's conclusions.
"We disagree with his central criticisms and we emphasize that all of
our original conclusions stand," said University of New Mexico biologist
John Grady."Comparing
dinosaur growth with the observed growth rate of living vertebrates
clearly shows that non-avian dinosaurs were mesotherms," added Grady,
using the term for an intermediate metabolism.Warm-blooded
land animals like mammals and birds have never achieved the size of the
biggest dinosaurs. But D'Emic said merely being warm-blooded would not
have prevented dinosaurs from getting large although they may have
needed adaptations to prevent their huge bodies from over-heating. "The
Earth was generally warmer during the time of the dinosaurs, and so
overheating could have been a problem for them. However, most large
dinosaurs had some hollow, air-filled bones in their skeleton and likely
had large air sacs in other parts of their bodies, just like birds
today," D'Emic said.This provided a "natural ventilation system" within their bodies that helped to keep them cool, D'Emic said.